1. Field of the Invention
The present invention relates to a pressure regulating unit for regulating pressure to be applied to liquid, a liquid supplying apparatus provided with the pressure regulating unit, and a liquid ejecting apparatus.
2. Description of the Related Art
A liquid ejecting apparatus is exemplified by an inkjet printing apparatus for ejecting ink (liquid) supplied from an ink tank (liquid container) through an inkjet print head (liquid ejection head) so as to print an image on a print medium. In, for example, a business-grade printing apparatus requiring an improved print speed as the printing apparatus, a large quantity of ink is ejected from the print head. In view of this, a large quantity of ink is required to be supplied to the print head. For this purpose, ink contained in the ink tank is pressurized by a pump or the like, and then, the pressurized ink need be supplied (pressure-supplied). In the meantime, ink, to which a negative pressure is applied, need be supplied to the print head for ejecting the ink from an ejection port in order to suppress the leakage of the ink from the ejection port.
Japanese Patent No. 3606282 discloses an apparatus for regulating the pressure of ink, the apparatus being provided with a pressure regulating unit on a supply path, through which the ink is supplied to a print head. The pressure regulating unit is adapted to regulate the pressure of ink to be pressure-supplied, to apply a negative pressure to the ink, and then, to supply the ink to the print head. The negative pressure is applied to the ink to be supplied to the print head so as to form a meniscus of the ink at an ejection port. The pressure regulating unit opens or closes a valve disposed on the supply path according to the negative pressure inside of the print head, the negative pressure being varied according to the ejection of the ink, in order to stabilize the negative pressure of the ink staying in the print head.
The pressure regulating unit disclosed in Japanese Patent No. 3606282 is configured such that, for example, in a case where ink is no longer pressure-supplied during the stoppage of a printing apparatus and during the exchange of the print head, a negative pressure to be applied to the ink is regulated to a low level. Therefore, the negative pressure to be applied to the ink staying in the print head becomes low during the stoppage of the printing apparatus and during the exchange of the print head, thus causing a possibility of leakage of the ink from the ejection port.